The invention relates to contaminated solution filtration apparatuses and machining solution filtration apparatuses for machining devices. More particularly, it is directed to a contaminated solution filtering apparatus and a machining solution filtration apparatus for a machining device which are not only capable of extending the life of a filter medium, thereby reducing the running cost of their filter devices, but also increasing the utilization of the machining device and facilitating maintenance.
FIG. 16 is a diagram showing a construction of an exemplary conventional apparatus for filtering a machining solution for a wire cut type electric charge machining device; FIG. 17 (a) is a partially sectional diagram showing a construction of a machining solution filter thereof; and FIG. 17 (b) is a plan view thereof. In FIGS. 16 and 17, reference numeral (1) designates a wire electrode; (2), a workpiece; (3), a machining vessel of the electric discharge machining device; (4), a machining solution filtration unit including a contaminated solution vessel for depositing a contaminated machining solution and a cleaning vessel for storing a clean machining solution that has been filtered; (7), a machining solution filter disposed within the cleaning vessel (6), the machining solution filter (7) communicating with the contaminated solution vessel (5) through a pipe (8); (9), a filter pump disposed in the pipe (8); (10), a pressure gauge for detecting a pressure within the machining solution filter (7); (11), (12), machining solution nozzles of the electric discharge machining device disposed so as to confront each other, both nozzles communicating with the cleaning vessel (6) through a pipe (13). The pipe (13) is provided with a supply pump (14).
FIGS. 17 (a) and (b) show a detailed construction of the machining solution filter (7). As disclosed in, e.g., Japanese Patent Unexamined Publication No. 73234/1984, the machining solution filter (7) has such a structure that a filter medium (18) is interposed between double-tubularly arranged perforated metal housings (15) (16) having a multiplicity of machining solution passing holes (17) on their sidewall surfaces; and that the upper and lower ends of the filter medium are interposed between plates (19), (20), each of which has a hole at its center. This machining solution filter (7) has the holes of the plates (19), (20) inserted by a cylindrical shaft (21) having a multiplicity of small holes (22) on the sidewall surface; sealed by packinqs (23), (23a); and fixed on a shaft fixing stand (25) by a nut (24). The cylindrical shaft (21) is connected to the pipe (8), while the machining solution filter (7) is usually located inside the cleaning vessel (6) and immersed into a clean machining solution.
An operation of the wire-rod electric discharge machining device having such machining solution filter device will now be described. The wire-rod electric discharge machining device machines the workpiece (2) using electric discharge energy generated by applying a voltage between the wire electrode (1) that has been inserted into a machining hole of the workpiece (2) and the workpiece (2) thereby to initiate discharge while supplying a machining solution therebetween (into the interelectrode gap) from the machining solution nozzles (11), (12). Machining scraps, which are substantially spherical being about several .mu.m or several tens of .mu.m in size, are produced during machining. Since the machining scraps lead to provoke unstable machining such as secondary discharge or concentrated discharge, or breakage of the wire electrode (1), the machining solution to be supplied between the wire electrode and the workpiece must be clean to stabilize the machining.
The machining solution sent from the cleaning vessel (6) to the machining solution nozzles (11), (12) through the pipe (13) by the supply pump (14) and then supplied to the interelectrode gap is thereafter received by the machining vessel (3) in the form of a contaminated machining solution containing machining scraps, discharged from a discharge pipe (3a), and fed back to the contaminated solution vessel (5) of the machining solution filtration unit (4). The contaminated machining solution is sent from the contaminated solution vessel (5) to the machining solution filter (7) by the filter pump (9) under pressure, introduced into the filter medium (18) while passing first through the small holes (22) of the cylindrical shaft (21) and then through the machining solution passing holes (17) of the inner perforated metal housing (15), filtered by the filter medium (18), discharged from the machining solution passing holes (17) of the outer perforated metal housing (16), and stored in the cleaning vessel (6). And the cleaned machining solution in the cleaning vessel (6) is supplied again to the interelectrode gap by the supply pump (14). Thus, this is how the machining solution is recycled. Since the volume of the machining solution supplied to the interelectrode gap is usually smaller than the volume of the machining solution filtered by the machining solution filter (7), the clean machining solution stored in the cleaning vessel (6) overflows into the contaminated solution vessel (5).
If the filter medium (18) is clogged and, as a result, the pressure within the machining solution filter (7) is so elevated as to exceed the tensile strength of the filter medium (18), then the filter medium (18) will be broken. For this reason, the pressure within the machining solution filter (7) is monitored by the pressure gauge (10) so that the filter medium (18) can be replaced at a predetermined pressure.
The conventional machining solution filtration apparatus for an electric discharge machining device is constructed as described above. In such an apparatus, the contaminated machining solution containing machining scraps whose size is relatively large is sent to the machining solution filter (7), thereby making the filter medium (18) susceptible to early clogging. Frequent clogging of the filter medium demands frequent replacement, thereby imposing the problem of raising the running cost. The replacement of a filter medium (18) requires extraction of the machining solution filter (7) which is immersed into the cleaning solution vessel (6), thereby not only splashing the machining solution but also blending the contaminated machining solution with the solution in the cleaning vessel (6). This suspends the machining until the cleaning vessel (6) is cleaned and keeps the machining device operative only for filtering, thereby imposing the problem of considerably reducing the utilization of the electric discharge machining device.
To overcome the above problems, i.e., to extend the life of the filter medium, a sedimentation tank (5a) communicating with the contaminated vessel (5) is arranged adjacent thereto as shown in FIG. 18. The contaminated machining solution from the machining vessel (3) is first held in the sedimentation tank (5a) to have its machining debris deposited therein and then sent to the contaminated solution vessel (5) (see Japanese Patent Unexamined Publication No. 73235/1984).
However, such an apparatus allows the large-sized machining scraps to be deposited relatively well, thus contributing to extending the life of the filter medium (18). However, this advantage will eventually be reduced to nothing unless the deposited machining scraps are removed periodically. Since the machining solution and its debris must be treated as industrial wastes, they cannot be drained into the sewage or the like. In addition, these wastes contain a large volume of water, thereby imposing another problem of being difficult in maintenance and handling. Furthermore, removal of the contaminated machining solution within the sedimentation tank (5a) takes the machining solution away therefrom in a volume corresponding to what has been removed, thereby requiring its replenishment. This not only elevates the running cost but also complicates the management of the specific resistance of the machining solution in case of the wire-rod electric discharge machining device.
The invention has been made to overcome the above circumstances. Accordingly, an object of the invention is to provide a contaminated solution filtration apparatus, which is simple in structure and efficient in filtration, and a machining solution filtration apparatus for a machining device which is not only capable of reducing its running cost by extending the life of a machining solution filter and improving utilization of the machining device by reducing machining solution filter replacements, but also easy in maintenance and readily repairable in the event of an abnormality.